1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device which has a ball grid array structure, package particularly to a semiconductor integrated circuit device having reliable on connections between the semiconductor integrated circuit device and a printed-wiring board on which the semiconductor integrated circuit device is mounted. Further, the present invention relates to a semiconductor integrated circuit device which is thin and has a high bending stiffness.
2. Discussion of Background
In recent years, the number of pins used in a semiconductor integrated circuit device has been increasing. Therefore, a package (hereinbelow, referred to as BGA 20 package) having a ball grid array structure is conventionally used, wherein conductive terminals having a spherical-shape, as an external connection terminal, are formed in a grid array. Such a BGA package is paid attention to because this package can satisfy increasing requirements for the packages, such as an increment in the number of pins, miniaturization, and a thin body.
FIGS. 9 and 10 respectively show structures of conventional BGA packages. The BGA package shown in FIG. 9 has a conductive pad provided on a principal surface of semiconductor chip 1 electrically connected to a conductors 6 through a conductive adhesive 9 at one surface side of a carrier base 3, and external output terminals 8 are provided on the conductor 6 at the other surface side of the carrier base 3.
On the other hand, the BGA package shown in FIG. 10 has a bonding pad provided on a principal surface of semiconductor chip 1 electrically connected to conductors 6 through bonding wires 7 to one surface side of a carrier base 3, and external output terminals 8 are provided on the conductor 6 at the other surface side of the carrier base 3.
In FIGS. 9 and 10, numeral 2 designates a die pad, and numeral 5 designates a sealing resin layer.
However, it has been pointed out recently that there is a problem of reliability on connection between such a BGA package and a printed-wiring board on which the BGA package is mounted. For example, in Nikkei Electronics (vol. 1997.7.28 (No. 695), pages 19 through 20), it is reported that because of a difference between a coefficient of thermal expansion of a semiconductor chip made of silicon 1 and that of an interposer (hereinbelow, referred to as carrier base) on which the semiconductor chip is directly installed, the largest deformation occurs at a central portion of BGA package, corresponding to a lower portion of the semiconductor chip 1, after a heat cycle test is conducted, and therefore solder balls connecting the package to a printed-wiring board, in which the package is equipped with, are apt to break by fatigue.
Specifically, as shown in FIG. 11, there was a phenomenon that a central portion at a side other than the side in which a semiconductor chip 1 is provided (namely, at the side in which external connection terminals 8 are provided) cambers when a carrier base 3 has a larger coefficient of thermal expansion than that of the semiconductor chip 1. The external connection terminals 8 of solder balls in the central portion receive a large load, therefore, that a crack is caused at an interface between the solder balls 8 in the central portion and the printed-wiring board 10 or in the solder balls 8 themselves. Thus the package was destroyed.
On the other hand, in order to evade affects of thermal stress caused by the difference between the coefficient of thermal expansion of the carrier base 3 and that of the printed-wiring board 10, it was proposed to use fiber-reinforced plastics for the carrier base 3. However, when the carrier base 3 made of fiber-reinforced plastics was used, the deformation of the central portion of BGA package caused by the difference of the coefficients of thermal expansion became large, whereby a problem of reliability of connections against deformation became conspicuous.
In the next approach, a ceramic was used for the carrier base 3, sacrificing the effects of thermal stress caused by the difference between the coefficient of thermal expansion of the carrier base 3 and that of the printed-wiring board 10. In this case, the difference between the coefficient of thermal expansion of the semiconductor chip 1 and that of the carrier base 3 was small and the deformation of the BGA package at the central portion thereof caused by the difference between the thermal coefficients became small. However, the deformation can not completely be eliminated and problems such as cracks and breakage in the solder balls 8 have been still existed though the extent of each problem was different.